Encoded content requires a “decoding” process in order to use the content. Some examples of encoded content include MPEG-1 MPEG-2 H264/AVC, WMA, MPEG4, JPEG2000, MP3, PDF, Windows Word, Postscript, etc, and their encrypted versions.
One prior art method for watermarking encoded content is to insert watermark signals in the structure and syntax elements. U.S. Pat. No. 6,687,384 is an example for embedding data in syntax elements in a coded bit stream such as MPEG-1 and MPEG-2. Such watermarks do not, however, survive format change or digital-analog conversion.
Another prior art method for watermarking encoded content is to embed a watermark by adding noise to the DCT coefficients for MPEG encoded content. An example of this approach is described by F. Hartung and B. Girod in “Digital Watermarking of MPEG-2 Coded Video in the Bit Stream Domain”, Proc. IEEE ICASSP, pp. 2621-4, April 1997. The method of Hartung and Girod does not use perceptual techniques.
Yet another prior art method for watermarking encoded content is to directly modify the encoded content. U.S. Pat. No. 6,373,960, hereinafter “Conover”, describes a watermarking method within an MPEG compressed video bit stream by modifying some DCT coefficient in such a way that the entropy encoded length of these coefficients remain unchanged after modification. No specific watermark embedding methods are specified in Conover. The methods for selecting watermark sites in Conover are limited to the coefficients with 0 run-zero. The coefficients of Conover are in the high frequency domain. The method of Conover includes no preprocessing phase nor is there any “alternative value” for actual watermark insertion in the later phase described. The concept of generating and using “watermark units” is nowhere disclosed or taught in Conover.
The prior art methods for watermarking encoded content does not have a pre-processor for producing “alternative values” for some parts of the encoded content. The prior art methods for watermarking encoded content exclude encoded content that is further masked, obfuscated, scrambled or encrypted (collectively “encrypted”).